The present invention relates to a corner tool for applying mastic material, compound, or other similar material to an external corner formed by the intersection of two sections of drywall which come together at substantially right angles, and are universally used in interior building walls.
Drywall heads for applying mastic compound to unfinished drywall corners are well known in the art. In one outside corner finishing method, a metal corner bead is secured to the outside corner edge of two adjoining drywall board sections using nails and/or screws after which a finishing coat of mastic or plaster material is applied to the outside corner. Many tools have been developed for the application of mastic material to outside corners, particularly outside corners which have been prefitted with a metal corner bead.
In a second outside corner finishing method, a first layer of fast set compound or mastic material is applied to the outside corner edge of two adjoining drywall board sections. An unfinished outside corner bead of metal, plastic, or other conventional material, is then applied to the fast set compound or mastic material contained on the outside corner edge of the adjoining drywall board sections. The unfinished corner bead preferably has a sheet of paper material adhered to the outer surface thereof. Such corner beads are generally referred to in the art as xe2x80x9ctaped-on cornersxe2x80x9d. The paper material extends a short distance beyond the vertical side edges of the unfinished corner bead such that the paper overlaps the adjacent portion of the drywall board section. An outside corner finishing tool is then used to apply a layer of mastic material to both sidewalls of the outside corner to bond the outside corner edge of the drywall and the taped-on corner.
U.S. Pat. No. 5,368,461 to Murphy is directed to an outside corner finishing tool for applying mastic, compound, or plaster material to outside corner edges formed by drywall board sections. The tool is a generally polygonal block-like enclosure of rigid material including a top wall and a bottom wall, a pair of concave inward front walls defining a 90xc2x0 inner corner adapted to fit an outside corner, and a back wall spaced from the front walls by a pair of spaced sidewalls. The back wall contains a spherical cavity for,receiving a ball socket connector. The cavity is connected to vertically oriented channels in the front wall. A pump-type applicator is connected to the ball socket connector and is operated to direct a regulated flow of mastic material into the spherical cavity. In turn, the mastic material is directed through the manifold to the vertical channels of the front walls for simultaneous application of mastic material along two adjoining wall board sections.
The finishing tool described in Murphy ""461 patent includes vertically oriented channels that extend between the top wall and the bottom wall of the tool. The channel members have a uniform width so that the tool may be moved in either vertical direction on the outside corner of the drywall to which the material is to be applied. Thus, the channels allow the tool to be moved bi-directionally, up and down, along the outside corner of the walls without removing the tool from contact with the wall as the mastic material is applied.
As shown in the Murphy ""461 patent, each channel has a uniform width throughout. In operation, mastic material enters the spherical cavity and is directed through each port into its respective dispersing cavity where it is then fed into the channels. The uniform width of the channels permit the tool to be moved in either direction, up and down, along the outside corner and thus permits the tool to be moved bi-directionally on the outside corner of the wall as the mastic material is applied.
Although the finishing tool described in the Murphy ""461 patent functions reasonably well to apply a strip of mastic material, the finishing tool suffers from several drawbacks. One of these drawbacks is the removable mounting of the head on to the ball joint connector. During use of the applicator head, the ball joint connector can become disconnected from the tool head if the tool head becomes snagged on the drywall as the tool head is applying mastic material. Further, the uniform width of the vertically oriented channels restricts the ability of the tool head to be used to smooth but a section of mastic material after the mastic material has been applied. In many situations, the viscosity of the material causes the strip to expand slightly after it has been applied. If the finishing tool of the Murphy ""461 patent is used to go over a strip of previously applied mastic material, the uniform channel may cause the strip to contact the other walls that define the channel and make a mess along the wall.
It is an object of the present invention to provide a drywall head for applying a metered amount of continuous, uniform and void-free mastic compound in ribbon form to adjacent walls of an unfinished corner to cement a variety of commonly used taped-on corners to an outside corner in a simple and efficient manner. It is a further object of the present invention to achieve this efficiency through the use of tapered flow channels within the inner walls of the tool. The channels taper from a leading edge of the tool to a trailing edge of the tool such that the tool is designed to be moved in a single direction along the corner. The taper of each channel allows the drywall head to gather and redistribute the strip of mastic compound on the drywall.
It is another object of the present invention to provide a drywall head for applying mastic compound of the type described which may be used with a pneumatic applicator for providing a constant and controllable flow of mastic material to the tool for application on the outside corner. When the present invention is utilized with the pneumatic applicator, a constant flow of material is supplied to the drywall head so that the material may be applied uniformly and in a constant manner to the outside corner. Use of the drywall head with the pneumatic applicator also reduces the labor effort required to apply the mastic material as physical pressure by the user is not relied upon. Furthermore, the combination of the drywall head with the pneumatic applicator allows for the one time, uni-directional application of mastic material to the unfinished corner.
The present invention is a drywall head for applying mastic compound to the adjacent walls of an unfinished corner. The drywall head is constructed of rigid material and comprises a block structure that has two inner guide surfaces set at a generally 90xc2x0 angle to each other, a top surface, a bottom surface, a back wall surface, an interposed flow chamber situated within the drywall head, and a ball socket. The ball socket opens into the interposed flow chamber, and the flow chamber further opens into ports within each inner guide surface. The ports within the inner guide surfaces open into uniquely constructed flow channels. The flow channels extend between a leading edge adjacent to the bottom surface of the tool, and a trailing edge adjacent to the top surface of the tool. The flow channels are defined laterally by a pair of retaining walls. The width of each of the flow channels at the leading edge is greater than the width of the channels at the trailing edge, as the retaining walls of each channel taper from the leading edge to the trailing edge. The trailing edge of each flow channel further contains a plurality of staggered teeth situated within the flow channel to aid in the uniform deposition of a metered amount of mastic material onto the unfinished corner, thereby providing an adequate amount of mastic to prevent blistering and create a void-free strip.
The drywall head of the invention further includes a ball assembly designed to fit into the ball socket located on the back wall surface. The ball assembly allows for pivotal movement of the drywall head in relation to a delivery tool, preferably a pneumatic applicator. The invention is designed so that the tool is used in a uni-directional motion. Application of the mastic material begins when the tool is placed at the juncture of the wall corner, typically near the ceiling. Application of the mastic material continues in one direction down the outside corner to the intersection of the wall corner and the floor.
The drywall head of the invention includes a C-spring assembly that provides a resilient means for biasing the drywall head in an upright, operating position relative to the pneumatic applicator that supplies a mastic material to the drywall head. The C-spring assembly orients the drywall head at a known position such that when the drywall head is removed from the corner, the drywall head returns to a known position. Further, the combination of the C-spring assembly and a series of guide wheels allow the drywall head to flex and follow the contour of the drywall as the mastic material is applied.
The outside corner head is designed to be used in one direction due to the difference in width of the channel from the leading edge to the trailing edge. If the tool were used in the opposite direction, the previously applied strip of mastic material would enter the head at the narrower trailing edge at exit at the wider leading edge. Thus, going over a previously applied mastic strip with the drywall head oriented in an opposite direction will result in destruction of the strip and a non-uniform width due to the increase in size of the channel.